There is a growing awareness and recognition of the importance of recycling, nevertheless, only a fraction of the generated municipal waste is actually recycled. It has been reported by the United States Environmental Protection Agency that in 2007, Americans generated 254 million tons of municipal waste. Of this only 63 million tons was recycled, 22 million tons composted, and 32 million tons was combusted to produce energy. That means that 137 million tons were simply discarded, mostly to landfills.
Economics is the primary reason for the limited amount of waste that is recycled. Simply speaking, if recycling does not generate a profit it is not done. The significant costs involved in recycling are sorting, transportation and the energy used in the sorting and transportation processes.
Various technologies have been developed over the years aimed at providing low cost useful products from municipal wastes.
U.S. Pat. No. 3,850,771 provides a process for processing waste wherein a portion of cellulose from the waste is separated (sorted) from the bulk of the waste and transformed into cellulose xanthate. The cellulose xanthate, being soluble, is uniformly distributed back into the waste and upon conversion back to the cellulose form, it binds the waste components. It is taught that the cellulose in the waste is essentially useless and may in fact be objectionable. These are the reasons that the patent teaches to remove a portion from the waste, convert it, and then remix it with the waste, and upon further treatment, the cellulose precipitates to form a binder.
U.S. Pat. No. 4,013,616 describes a method of using comminuted municipal or industrial waste as a filler for thermosetting or thermoplastic resins such as polyethylene and using the filled resin to make a useful product. The process requires a presorting of the waste into light and heavy fractions. Moreover, the patent teaches that the plastics in the original waste are not suitable as binding agents. The components making up a typical municipal waste are set forth in Table 1 of the patent.
U.S. Pat. No. 4,772,430 describes a process for compacting solid waste containing at least 10% by weight thermoplastic materials using an extrusion molder to obtain high-density rod-like masses or pellets. The rod-like masses or pellets consist of non-homogenous aggregates of miscellaneous waste materials and because of the process conditions, the plastic is concentrated at the peripheral portion of the composite to form a plastic solidified layer, like a crust.
U.S. Pat. No. 4,968,463 describes a method focusing on disposing of plastic waste wherein it is important that the thermoplastic content be over 65% by weight and the water content be less than 3% wherein optionally adding filler (which can also be a waste) and coloring materials. The product is characterized by having a bending rupture stress (flexural strength) of 35-50 N/mm2 and is processable with machine tools used for wood.
U.S. Pat. No. 5,217,655 describes a composite product obtained by first granulating a mixture of plastic and fibrous material, e.g. a commercial, municipal or industrial waste from which, preferably, metal has been removed, and then heating the mixture in stages from about 100-204° C. while continuously mixing in an extruder. The composite material may contain at least 50% thermoplastic material and is described as having high impact properties, high compression strength, may be coated with coloring agents and may be used for industrial posts, beams and construction columns.
U.S. Pat. No. 6,017,475 describes a process utilizing a hydrolyzer for the complete hydrolysis of ligno-cellulose matter in waste. The process yields sterile cellulose pulp aggregates having traces of metals, plastics etc., macroscopically mixed in the aggregates. The aggregates are separable into pure cellulose pulp and a residual mixture containing inorganic pulp. The cellulose pulp and/or the residue may be further extruded, optionally with plastics or other additives to form useful products. Some products of the process are described in WO 2005/092708 and US2004/0080072.
U.S. Pat. No. 6,253,527 describes a method of compression molding of waste or filler particles that are bound together and encapsulated by a thermoplastic binder. The composite material is prepared by mixing particles of thermoplastic and waste or fillers; using high intensity mixing to frictionally heat the particles bringing the thermoplastic particles to a molten state where they coat and encapsulate the waste or filler particles. The molten mass is then compression molded.
U.S. Pat. No. 6,423,254 describes a method for manufacturing products from various types of waste materials comprising about 80% polyolefins and about 20% other thermoplastic polymers. The waste may be used in combination with raw materials such as wood, plastics, metals, heat-stabilizers and blowing agents.
KR 2003/0014929 describes a composite material obtained from waste from which metal was sorted out. The composite material comprises between 30-70% thermoplastic materials after sorting out metals, inter alia, because the metals cause problems in the grinding process.
WO 2006/079842 describes a method for processing clinical waste containing between 10% and 50% thermoplastic material, about 20% water, and the rest consisting of mainly cotton, adhesives, rubber and metal. The product is moldable and has a density of 200-500 Kg/m3.
WO2006/035441 describes a method of encapsulating pieces of waste with melted plastic by heating and mixing.